In modern vehicles, including automobiles, trucks, planes, boats, etc., it is common that a need exists for communicating digital data within the vehicle, typically between a computer or processor in the vehicle and some hardware device in the vehicle. Typically, this is accomplished with copper cabling. Unfortunately, the electrical environment of vehicles is not always as controllable as in stationary applications (like in an office setting), which can lead to transient and/or spurious voltages or currents being communicated along the copper cabling. This can damage the computer/processor and/or the hardware device. This can also corrupt the integrity of the data communication. One ready example of such a problem is the transient voltage and currents that can be developed in a vehicle by a lightning strike. This lightning problem is particularly acute for aircraft, as they often are required to operate in the near presence of lightning and the movement of the aircraft through the air can create conditions that actually increase the chances of the aircraft being struck by lightning. When lightning strikes an aircraft, the transient voltages/currents developed within the aircraft can be substantial and if allowed to propagate to the computer/processor and/or hardware device, the damage thereto can be significant.
Known attempts to arrest or isolate voltages and currents developed within vehicles as a result of a lightning strike are generally inadequate. One problem with known isolation solutions is that they are generally too large for good use in vehicles (including aircraft). Another drawback to existing isolation solutions is that the data transmission rates for such arrangements are unacceptably low. Typical optical isolators operate at kilobits per second rates and do not support differential signals. Moreover, transformer isolation techniques have generally poor application in vehicles as they introduce losses and distortions unacceptable for extended cable runs (greater than 5 meters).
For example, with the proliferation of commercial standards recently, the military is attempting to adopt a number of high-speed interconnect protocols that have physical implementations that are not compatible with aircraft lightning environmental requirements. The high-speed protocols with DC coupling requirements, digital visual interface (DVI), for example are the most difficult to integrate as a communications link between two enclosures separated by more than two or three feet. When an aircraft is struck by lightning, as much as 200,000 amperes may pass through the skin of the metal aircraft. This high current can cause voltage potential differences between the enclosures to be in excess of 300V and thus 600 amperes may flow along the surface of the shielded cables between enclosures. When this high current flow happens in a cable shield, common mode voltage threats can exceed 60V, depending on the cable length, transfer impedance, number of cables in a given bundle, etc. Today's high-speed protocols that use differential signaling typically can be damaged by as little as 0.5V. Due to the low level signal involved with a communications link, typically as low as 800 mVp-p from a single source, traditional surge suppression techniques with load capacitances in the thousands of picofarads are not compatible with signal integrity constraints and requirements. Known ESD (Electro Static Discharge) suppression devices compatible with low voltage differential signaling cannot handle the induced energy from a lightning strike either.
Accordingly, it can be seen that a need yet remains for an isolation system or device that can communicate high-speed data, but yet can provide highly effective electrical isolation to arrest or isolate transient or spurious voltages and currents that can develop in vehicles. It is to the provision of such an isolation device that the present invention is primarily directed.